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761.
Under certain conditions an intense kinetic plasma jet is observed to emerge from the apex of laboratory simulations of coronal plasma loops. Analytic and numerical models show that these jets result from a particle orbit instability in a helical magnetic field whereby magnetic forces radially eject rather than confine ions with sufficiently large countercurrent axial velocity. 相似文献
762.
Ansu Alok Kumar Sharma R. K. Hagos F. Y. Tripathi D. Tyagi V. V. 《Journal of Thermal Analysis and Calorimetry》2021,143(3):1881-1892
Journal of Thermal Analysis and Calorimetry - In the present investigation, a novel composite of Polyethylene glycol (PEG) with molecular weight 10,000 (10 k) and aluminum oxide... 相似文献
763.
A method for the preparation of highly conductive and stable organic-inorganic nanocomposite polyelectrolyte membranes with controlled spacing between inorganic segment and covalently bound sulfonic acid functional groups has been established. These polyelectrolyte membranes were prepared by condensation polymerization of the silica precursor (tetraethylorthosilicate) in dimethylacetamide in the presence of poly(ethylene glycol) (PEG) of desired molecular weight, and sulfonated poly(styrene-co-maleic anhydride) was attached to the polymeric backbone by hydrogen bonding. Molecular weight of PEG has been systematically changed to control the nanostructure of the developed polymer matrix for studying the effects of molecular structure on the thermal as well as conductive properties. These polyelectrolyte membranes were extensively characterized by studying their thermo-gravimetric analysis (TGA), ion-exchange capacity (IEC), water content, conductivity, methanol permeability, and current-voltage polarization curves under direct methanol fuel cell (DMFC) operating conditions as a function of silica content and molecular weight of PEG used for membrane preparation. Moreover, from these studies and estimation of selectivity parameter among all synthesized membranes, 30% silica content and 400 Da molecular weight of PEG resulted in the best nanocomposite polyelectrolyte membranes, which exhibited performance comparable to that of the Nafion 117 membrane for DMFC applications. 相似文献
764.
An isomer-divergent synthesis of naturally occurring pericosines A and B is described starting from a known D-ribose derived ene-diol in 35% and 41% overall yields respectively of which the latter is the best synthetic method reported for pericosine B. The key features of this synthesis include the stereoselective NHK vinylation of the terminal aldehyde to the versatile diolefinic chiral intermediate and elegant conversions of the same to the corresponding final products via RCM (Ring Closing Metathesis). 相似文献
765.
Conformational flexibility plays a central role in allosteric transition of proteins. In this paper, we extend the analysis of our previous study [S. Tripathi and J. J. Portman, Proc. Natl. Acad. Sci. U.S.A. 106, 2104 (2009)] to investigate how relatively minor structural changes of the meta-stable states can significantly influence the conformational flexibility and allosteric transition mechanism. We use the allosteric transitions of the domains of calmodulin as an example system to highlight the relationship between the transition mechanism and the inter-residue contacts present in the meta-stable states. In particular, we focus on the origin of transient local unfolding (cracking), a mechanism that can lower free energy barriers of allosteric transitions, in terms of the inter-residue contacts of the meta-stable states and the pattern of local strain that develops during the transition. We find that the magnitude of the local strain in the protein is not the sole factor determining whether a region will ultimately crack during the transition. These results emphasize that the residue interactions found exclusively in one of the two meta-stable states is the key in understanding the mechanism of allosteric conformational change. 相似文献
766.
B. K. Rana R. M. Tripathi J. S. Meena S. K. Sahoo R. Topno A. K. Shukla V. D. Puranik 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(2):347-352
In the environs of uranium mining, milling and processing facilities and in the uranium mineralized terrain, a little higher
ambient radon concentration and gamma radiation level may be expected in comparison with natural background. The present study
gives a brief account of atmospheric radon concentration, gamma absorbed dose rate and radiation dose received by the members
of public in the vicinity of Narwapahar uranium mine. The ambient radon concentration in the air in the study area was found
to vary from 5 to 107 Bq m−3 with geometric mean of 24 Bq m−3 and geometric standard deviation of 1.74 Bq m−3. The measured gamma absorbed dose rate in air at 1 m above the ground ranged from 87 to 220 nGy h−1 with an overall arithmetic mean of 128 ± 18.5 nGy h−1. The mean annual effective dose received by the members of public from inhalation of radon and its progeny and external gamma
exposure was estimated to be 0.32 mSv year−1, which is comparable to other reported values elsewhere. 相似文献
767.
S. Chinnaesakki Manish Chopra Sanjeev Kumar Vishal Arora S. J. Sartandel S. V. Bara R. M. Tripathi V. D. Puranik B. S. Bajwa 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(3):885-892
This study presents the high purity germanium (HPGe) gamma spectrometric measurement of natural radioactivity mainly due to
226Ra, 232Th and 40K in soil samples collected in Ferozepur and Faridkot district of Punjab, India. 226Ra activity varied from 28.6 to 51.1 Bq kg−1 with the mean of 39.7 Bq kg−1. The range and mean activity of 232Th were 42.9–73.2 and 58.2 Bq kg−1, respectively. 40K activity was in the range of 470.9–754.9 Bq kg−1 with the mean of 595.2 Bq kg−1. The air kerma rate (AKR) at 1 m height from the ground was also measured using gamma survey meter in all the sampling locations,
which was ranging from 92.1 to 122.8 nGy h−1 with the mean of 110.6 nGy h−1. The radiological parameters such as Raeq and activity index of the soil samples were also evaluated, which are the tools to assess the external radiation hazard due
to building materials. The mean and range of the Raeq values were 168.7 and 132.9–210.4 Bq kg−1, respectively, whereas the activity index varied from 0.5 to 0.8 with the mean value of 0.62. These indices show that the
indoor external dose due to natural radioactivity in the soil used for the construction will not exceed the dose criteria.
The AKR was also evaluated from soil activity concentration and altitude correction of cosmic radiation contribution. The
statistical tests such as Pearson correlation, spearman rank correlation, box and whisker plot, the Wilcoxon/Mann–Whitney
test and chi-square test, were used to compare the measured AKR with evaluated AKR, which indicates good correlation. 相似文献
768.
P. N. Pathak D. R. Prabhu M. Bindu S. C. Tripathi V. K. Manchanda 《Journal of Radioanalytical and Nuclear Chemistry》2011,288(1):137-142
The primary purpose of this study was to understand the alpha radiolytic degradation behavior of N,N-dihexyl octanamide (DHOA) vis a vis tributyl phosphate (TBP) solutions in n-dodecane under plutonium loading conditions. These studies were carried out as a function of dose on different Pu loaded
samples (containing 0.002-10 g/L Pu) from 4 M HNO3 medium. These Pu loaded solutions were evaluated for stripping behavior by contacting with 0.5 M NH2OH at 0.5 M HNO3 solutions. Organic phase analysis was carried out by gas chromatography (GC) and by visible spectrophotometry. These studies
clearly indicated that Pu stripping becomes difficult with increased dose in the case of TBP system. On the other hand, no
such problem was observed in DHOA system during stripping of plutonium, thereby indicating that DHOA is a promising candidate
for the reprocessing of high burn up Pu rich spent fuels. 相似文献
769.
One pot synthesis of the butenonyl-C-β-d-glycosides with malononitrile in the presence of K2CO3 in water under mild and green reaction conditions leading to the formation of small library of multifunctional biphenyl methyl-C-β-d-glycosides in good yields has been reported. The reaction is equally applicable with the substrates having different glycosyl pyranoses and aromatic rings with different substituents. 相似文献
770.
Bhattacharyya K Varma S Tripathi AK Vinu A Tyagi AK 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(44):12310-12325
Nanoparticles of Ti(0.95)V(0.05)O(2) were found to be impregnated in the hexagonal channels of the MCM-41 host, with a distribution of some particles on the surface, thus leading to an effective variation in the particle size as a function of loading host MCM-41 matrix. These catalysts were subjected to the photocatalytic degradation of alkenes under the ambient conditions in which the photocatalytic activity varied as a function of the loading percentage of Ti(0.95)V(0.05)O(2) in the host MCM-41.This is explained in light of the structure-activity correlation, and the better catalytic activity can be attributed to an electronic interaction between the host and guest molecules, as established from X-ray photoelectron spectroscopy. To understand the mechanistic aspect of the photooxidation of ethylene on the vanadium-doped titania dispersed in the MCM-41 matrix, extensive in situ FTIR experiments were undertaken. The intermediate species produced on bare Ti(0.95)V(0.05)O(2) are different from that produced on the Ti(0.95)V(0.05)O(2)/MCM-41 surface. Moreover, different intermediates were produced during ethylene oxidation under UV and visible irradiation, thus leading to different rates. The ethylene decomposition over bare Ti(0.95)V(0.05)O(2) occurs by means of formation of ethoxy groups, transformed to acetaldehyde or enolates, subsequently to acetates, and then to CO(2) under both UV and visible irradiation. However, in the case of Ti(0.95)V(0.05)O(2)/MCM-41 catalyst with UV irradiation, the adsorbed acetaldehyde thus formed undergoes aldol condensation over the Lewis acid sites to lead to the formation of crotonaldehyde, which is subsequently oxidized to acetate and consequently to CO(2). It was observed that during visible irradiation labile ethyl acetate is produced either by the Tischenko reaction or by the reaction between the labile acetic acid and the unreacted ethoxy groups. The ethyl acetate produces acetic acid monomer, which is oxidized to CO(2). Furthermore, in this work the effects of particle size on the intermediate species were also studied. 相似文献